The invention is directed to suppressing smoke generation in hot melt adhesive compositions.
Hot melt adhesive compositions are used in many applications in a variety of industries. In many of these applications, a government body requires the article in which the adhesive is present to meet one or more flammability or fire retardant tests. UL 900, for example, is a current Underwriters' Laboratory (UL) test method that imposes stringent requirements on the amount of smoke, flame and spark emissions that can be generated by burning filter packs. Filter packs are often constructed from glass fiber webs and a hot melt adhesive composition. Many hot melt adhesive compositions are inherently flammable, at least to some extent. Thus, since glass fiber webs are essentially noncombustible, the binders and adhesive compositions present in the construction may potentially represent a major factor in the amount of flame and smoke generated by the filter during combustion.
Various attempts have been made to improve the flame retardant and/or smoke suppressant properties of hot melt compositions including formulating the compositions with flame retardant and/or smoke suppressant additives. Conventional flame retardant and smoke suppressant additives include, e.g., phosphorus-containing compounds such as a phosphoric acid ester, ammonium polyphosphate and red phosphorus, halogen-containing compounds such as tetrabromobisphenol A, decabromodiphenyloxide and chlorinated polymers, and metal compounds such as magnesium hydroxide, aluminum hydroxide and zinc borate. Halogen-containing compounds exhibit good flame retardant properties and are widely used. However, compositions formulated with halogen-containing compounds tend to generate undesirable levels of smoke when combusted. Other inorganic flame retardant additives include hydrated inorganic compounds, which function by absorbing heat and evolving water vapor or steam. The vapor or steam dilutes the combustible gases that are generated during a fire.
Although advances have been made in achieving hot melt adhesive compositions that exhibit good flame retardant properties, the amount of smoke generated by hot melt adhesive compositions remains at undesirably high levels for many applications. It is often difficult to formulate compositions to simultaneously exhibit good flame retardant properties and smoke suppressant properties. The additives that impart smoke suppressant properties to a composition tend not to be flame retardant.